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How does delay-based pitch-shift work?

Hey! I guess this is a quite easy question since the technique exists pretty long: I want to build a pitch-shifter based on delay. How does it work? I assume folloeing:
- building a tape-delay (which changes pitch when delay-time is changed)
- sawtooth modulation of delay-time
Anything useful about my guess? Please help! Thank you!

yep you're on the right track-- it's also related to the doppler effect, when an approaching sound-source's apparent pitch increases (it's delay time decreases because sound takes less time to reach the listener), and vice-versa

Hi
as the delayed repeats 'move further away' (ie, delay time increases) the period of the frequencies increases, creating the illusion of a fall in pitch and vice versa. It's obvious how this works in the real world, but perceptually? I haven't a clue! There's a great example of how to achieve this effect in MaxMSP on youtube, with helpful explanations of relevant formulae etc, by 'dude837'

Just one fact which actually made me think about all that:
In an interview MOUSE ON MARS say "These are two delays which run into feedback quickly. And with the speed of the feedback-rate you can control the pitch." - This really confused me. :)